This invention relates to a lubricating oil composition. More particularly, this invention relates to a synthetic lubricating oil composition. Still more particularly, this invention relates to a synthetic, ester lubricating oil composition.
Synthetic lubricating oils comprising simple esters, complex esters and/or polyesters, as base oil stocks are well known in the prior art. In fact, due to the unique physical characteristics of these materials, the synthetic, ester lubricating oils have been widely used in those areas wherein oils are subjected to extreme temperature variations, such as in aircraft engines and the like. These ester base oils do not, however, inherently exhibit high load carrying ability and cannot be used, without modification, where a high degree of lubricity is required. Also, the synthetic ester oil compositions are subject to oxidative degradation and cannot be used, without further modification, for long periods under oxidizing conditions. Moreover, most, if not all, synthetic ester lubricating oils, which have been modified through the use of load augmenting additives, are not compatible with silicone elastomers commonly used in jet engines and accessories and, therefore, cannot be used in contact with such materials, at least at elevated temperatures, for long periods without further modification thereof. Further, the synthetic ester lubricating oil compositions tend to be corrosive and will, indeed, attach some metals used in turbo-jet and turbo-prop engines, such as copper and magnesium, when used in contact therewith without the use of further additives.
It is also well known that any one of the aforementioned deficiencies of the base oils can be avoided through the proper selection of one or more additives known to be effective in overcoming any particular deficiency. In fact, it is often possible through the proper selection and combination of additives to overcome several known deficiencies of the ester base oil stocks. It has not, however, heretofore been possible to overcome all of these specified deficiencies in a single formulation or even to obtain a satisfactory balance which would, then, permit a relatively broad range of application for a single formulation. As a result, it has, heretofore, been necessary to formulate different compositions for different applications and in some cases, at least, these compositions are only marginally acceptable for the designed application since they do not exhibit the optimum balance of properties required therefor.
One reason for the aforementioned inability to produce a single lubricating composition having a relatively good balance of properties is that as to certain deficiencies, the various additives must perform competing functions and when such additives are blended one or more will dominate in performance at the expense of the remaining additives. Another reason for this inability is that, in some cases at least, the various additives are chemically incompatible and when such additives are blended chemical reaction and/or decomposition result in loss of additive function and in some cases, at least, will result in engine deposits. In this regard, it is well known that such deposits can cause serious operating problems ranging from seal leaks to engine failures. Such deposits are therefore, undesirable and should be avoided if at all possible.
In light of the foregoing, it is believed that the need for a synthetic lubricating oil composition having an improved balance of properties is readily apparent. It is also believed that the need for such a synthetic lubricating oil composition which can be used without undesirable engine deposits or at least with a minimum of such deposits is also readily apparent.